Hollow tap



Oet.l30, 1945.V E.`M. TUCKER ETAL p 2,388,022

` HOLLOW rrAP `Iiled Deo. 21, 1943 i l l l 5mm 1m Patente-i 0er. 3.o, i945 UNITEDv srA'rss 'PAjrsNoFrra neraow me Emmitt M. Tucker and Emmitt M. Tucker, Jr.,

Grass Valley, and Joseph' M. Tucker, Long Beach, Calif., assignors of one-tenth to .lohn J. Looser, Grass Valley, Calif.

Application December 21, i943, Serial No. 51551582 I 4 Claims. (Cl. l0-141) This invention relates to thread-cutting taps, one object being to provide a. tap so constructed Vthat the shavings as cut by the'advance of the e shank as at E for strength. Cut in the tap at the tap will be removed from the hole without the i `need of employing deep -and widey full-.length flutes such as are found in thevconventional tap.

'I'he elimination of such flutes as the sole means of, carrying olf shavings or chips 'not only strengthens the tap,- but avoids thev working of the chips being carried away against the threads as'they are cut, and which tends to mutilate'the threads.

Another object is to construct the tap so that there is a' minimum of friction between the cut threads `.and the tap when retracting the latter, so that there is no chance of damaging the threads. y

This feature is made possible and commercially practicable by the provision' of a novel method of making the tap, and which forms still another object of the invention.l A,further object of the invention is to prov-ide a simple and inexpensive device, and yet one Awhich will' be exceedingly effective for the purpose for which it is designed.

These objects .we accomplish by means of such head end thereof is a diametral slot 1 which exltends from the outer edges of the adjacent threads to the bore 5, and lengthwise of the tap from its outer end to a termination adjacent the first full-depth thread, which is of course `the point at which the thread cutting operation of the tap ceases.. The leading edges L of this slot are the cutting edges of the tap, .and are disposed so as to be radially out from the trailing edges of the slot, this being done by the method described later.

From the rear ends of the slot on opposite sides of the tap, narrow grooves lof rectangular form may be cut through the threads to the rear end thereof; the leading edges of these grooves (which replace the usual .wide and 'deep flutes) being also radially out relative to their trailing edges.

The cutting slot l, as shown in Fig. l, extends generally in a direction axially of the tap, and the leading edge flares away from the axial line of i the tap, as shown. l

structure and relativel arrangement of parts as speciilcation and claims.

In the drawing, similar characters of reference indicate corresponding parts in the several Vwill fully appear` by a perusal of the following In Fig, 4, however, the slot 'la cut in the tap la is shownas extending diagonally relative to the' axis of the tap; the leading and. cutt-ing edge sloping in the direction of cutting rotation of the tap. Also in Fig. 4, the longitudinal groove or flute beyond the slot is eliminated. In either case, the chips orshavings cut in the work by the rotation and advance of the tap, fall orare deflected into the central bore, where they are of Figure 1 is alongitudinal view of the improved ,l

Eigure 2 is a head end view of the same. Figure 3 is a butt end view of the tap.

Figure 4 is a fragmentary elevation showing.

a modified form of ilute.

Figures 5 to 8 are diagrams illustrating certain 4steps in the vmethod of making the tap.

' Referring now more particularly to` the characters of reference on the drawing, the tap comprises a body l having asquare shank 2 at its bu end forY engagement with a chuck.

The body for the major portion of its length is provided with threads 3 of predetermined size and pitch; a few of the threads at the head end of the tap being intersected as usual by the taperingof the body at that end, as at 4,' so that these threads gradually diminish in depth and finally disappear as the taper passes inwardly of the plane of the base of the threads. Thus far, the

arrangement is continual and standard.

The tap from end to end is provided with a relatively large bore 5 which is reduced at the width of a few thousandths course kept from possible contact with the iinished threads as they are cut. The grooves or E flutes 8 if provided merely formdclean-cut or iinishing elements for the .cut threads, and do not carry lany shavings or chips to mar or mutilate 'saidahreads as is the case with the conventional tap.

The radial difference between the leading and trailing edges of the. slots and flutes, and the `elimination. of material friction when retracting the tap, is obtained by the following manufacturing procedure. A hardened block 9 is tapped as at Il! to the size and length of the tap to be made, after which the block is cut through diametrally of the tapped hole as at Il, for the of an inch, and then providing separate block sections l2. The threaded but unslotted tap I, prior to tem-f pering, is then placed between the blocks, after which pressure is exerted against the block sections I2 on opposite sides of and at right angles to the cut, to force said sections toward each other and close the gap, as shown in Fig. '7.

This obviously results in deforming the tap so the threads from the l Letters Patent that it is slightly .though symmetrically out of round, with its major diameter4 D, however, remaining normal. 'I'he blooks-are then separated and the tap withdrawn.A The slot 1 is then out in the tap on a bias to diametral line D, and so that'the leading edges of the slot will lie on said line. Due to the out-of-round `formvof the tap,

,the trailing edges` of the slot (and flute B) will be radially inward of the leading edges, as will all of trailing to the leading edge.

As' a result, the tap when engaging the iinished threads, only contacts the same atI diametrally opposed points, and hence can be retracted with a minimum of resistance and without possible damage to the threads.

From the foregoing description it will be readily seen that we have produced sucha 'device as substantially 'fuliis the objects of the invention as set forth herein. l

Wnue this specmcanon sets, form in detail the present and preferred construction of the device,

assenza l l. A tap comprising 'a body, threads on the still in practice such 4deviations from such detail may be resorted to 'as do not form a departure from the spirit of the invention, as" defined by n the appended claims.

'Having thus described ourinvention, what we claim as new and useful and desire to secure by body adjacent its forward end, the body at said end having a diametral slot cut therethrough and through the threads lengthwise of the body and 'having its leading edge radially out from its trailing edge, land the'body having a central bore extending from the outer end of the body to the rear end of and intersecting the slot.

2. A tap as in claim l1,-in which the threads adjacent the forward end of the .body become in#- creasingly shallow in depth toward said end the .I

slot extending back tothe full-depth threads.

3. A tap as in claim l, in which the slot is cut "on a bias relative to the axis of the tap, with the leading edge of the slot sloping in the direction of cutting rotation oi' the tap. i

4. A tap comprising a threaded body of slightly` oval shape in cross section. av diametre] slot cutinto the working end of the body to form a cutting flute, the leading edge of which lies in a plane along the major diametral axis of the body.v

inner end of and a bore through the body, the which bore opens into the slot.

` EMm'r'r M.' TUCKER.

EMMI'II M. TUCKER, JR. JOSEPH M.' TUCKER.V 

